System setup
First, what is the least capable speaker in your system were it concern the frequency response. Check the spec's on your speakers. Set the crossover 10 higher. Turn the crossover on the sub all the way up or turn is to zero. Remember the LFE channel carries information up 120 Hz. So, think of the .1 channel as a production channel for movies engineers and think of the sub as a playback channel. Turning the sub all the way up allows the sub to get all the .1 information, a lower setting than 120, will loose some of the .1 material. Set all speaker to small, even if they are tower speakers and let the sub do what subs do best, handle the low frequencies. For 2 channel listening the tower can be changed to large. I hope this is of some help. Very few tower speaker can handle the lower frequencies as well as a good sub! I know, but I paid good money for my towers, sob, sob. lol.